Conventionally, a scanning electron microscope is sometimes attached to a scanning tunneling microscope (STM). Secondary electrons are detected by the scanning electron microscope (SEM). The specimen surface is searched for a region of interest. This region is scanned by the STM, thus obtaining an STM image. It is also common practice to scan the conducting tip of the STM with an electron beam and to display an SEM image. This enables the operator to confirm and evaluate the shape of the tip.
An STM creates a topographic image of a specimen surface. On the other hand, in a SEM, the secondary electron emission rate differs according to the tilt of the specimen surface. An image representing the topography of the specimen surface is obtained, utilizing this difference in the secondary electron emission rate. Also, an image representing the atomic composition of the specimen surface is derived by making use of the fact that the secondary electron emission rate differs according to the composition of the specimen. In this way, the STM image and the SEM image offer different kinds of information. Therefore, one sometimes wants to compare these two kinds of images. In some cases, one wants to find a point of interest while observing an STM image and to produce Auger electrons from this point for analyzing it. In order to make such a comparison, it is necessary that they lie in the same field of view. It is not easy for the conventional STM equipped with an SEM to bring the fields of view of both images into agreement. Furthermore, a gross difference in resolution between these two kinds of microscopes makes it difficult to compare both images.
Additionally, the conventional instrument needs separate devices (e.g., an electron gun, electromagnetic lenses, deflectors and a scanning power supply) to obtain secondary electron images. Therefore, if observation of secondary electron images is made possible, then the cost of fabricating the whole instrument is inevitably increased.
Moreover, it is necessary for the prior art instrument to illuminate the specimen with an electron probe having a sufficient amount of electrical current on the order of 0.1 to 1 nA in order to obtain Auger images. As a result, the diameter of the electron probe amounts to approximately 500 Angstroms. This makes it impossible to have a high-resolution Auger image. Where it is attempted to analyze a certain point in an STM image by Auger spectroscopy, it has been impossible to analyze the energies of Auger electrons by directing an electron beam to a point on the specimen which corresponds to the certain point.